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Path: utzoo!utcsstat!geoff
From: geoff@utcsstat.UUCP (Geoff Collyer)
Newsgroups: net.bugs
Subject: scanf returns short count on null field(s)
Message-ID: <2069@utcsstat.UUCP>
Date: Thu, 6-Sep-84 21:35:12 EDT
Article-I.D.: utcsstat.2069
Posted: Thu Sep  6 21:35:12 1984
Date-Received: Thu, 6-Sep-84 21:53:27 EDT
Organization: U. of Toronto, Canada
Lines: 41

At least under format %[, the count scanf returns is too low by the
number of null fields read.  This bug appears in the v7 and 4.2bsd stdio
implementations, so it is likely in all AT&T scanfs, though I haven't checked.

I have added this to the BUGS section of scanf(3S):
---
.PP
The
.I scanf
functions return a count which is too low by the number
of null fields scanned.
---

The follow program demonstrates the bug:
---
#include <stdio.h>

main()
{
	char line[200];
	char s1[200], s2[200], s3[200], s4[200], s5[200];

	while (fgets(line, sizeof line, stdin) != NULL) {
		s1[0] = s2[0] = s3[0] = s4[0] = s5[0] = 0;
		printf("sscanf returned %d\n",
			sscanf(line,
			"%[^:\n]:%[^:\n]:%[^:\n]:%[^:\n]:%[^:\n]\n",
			s1, s2, s3, s4, s5));
		printf("tokens: `%s' `%s' `%s' `%s' `%s'\n",
			s1, s2, s3, s4, s5);
	}
	exit(0);
}
---
Try the following input:
---
a:b:c:d:e
:b:c:d:e
::c:d:e
:::d:e
---